A roller bearing is composed of an outer ring, an inner ring, a plurality of rollers arranged between the outer ring and the inner ring, and a retainer retaining the plurality of rollers in general. The retainer is composed of one integrated, that is, annular component in general.
Since a roller bearing to support a main shaft of a wind-power generator provided with a blade for receiving wind has to receive a high load, the roller bearing itself is large in size. Thus, since the components such as a roller and a retainer that compose the roller bearing are large in size also, it is difficult to produce and assemble the components. In this case, when each component can be split, the production and assembling become easy.
Here, a technique concerned with a split type retainer split by a split line extending along a rotation axis of a bearing, in a roller bearing is disclosed in European Patent Publication No. 1408248A2. FIG. 39 is a perspective view showing a retainer segment of the split type retainer disclosed in the European Patent Publication No. 1408248A2. Referring to FIG. 39, a retainer segment 101a includes a plurality of column parts 103a, 103b, 103c, 103d, and 103e extending along a rotation axis of a bearing so as to form a plurality pockets 104 to house rollers, and connection parts 102a and 102b extending in a circumferential direction so as to connect the plurality of column parts 103a to 103e. 
FIG. 40 is a sectional view showing a part of a tapered roller bearing containing the retainer segment 101a shown in FIG. 39. Referring to FIGS. 39 and 40, a constitution of a tapered roller bearing 111 containing the retainer segment 101a will be described. The tapered roller bearing 111 includes an outer ring 112, an inner ring 113, a plurality of tapered rollers 114, and a plurality of retainer segments 101a, 101b, and 101c retaining the plurality of tapered rollers 114. The plurality of tapered rollers 114 are retained by the plurality of retainer segments 101a and the like in the vicinity of a PCD (Pitch Circle Diameter) 105 in which the behavior of the roller is most stable. The retainer segment 101a retaining the plurality of tapered rollers 114 is connected such that the column parts 103a and 103e positioned outermost in the circumferential direction abut on the circumferentially adjacent retainer segments 101b and 101c having the same configuration. The plurality of retainer segments 101a, 101b, and 101c are continuously lined with each other and assembled in the tapered roller bearing 111, whereby one annular retainer is formed in the tapered roller bearing 111.
According to the European Patent Publication No. 1408248A2, after the retainer segments formed of a resin have been arranged so as to be continuously lined with each other, a circumferential range of a last clearance generated between the first retainer segment and the last retainer segment is to be not less than 0.15% of a circumference of a circle passing through the center of the retainer segment but less than 1% thereof. In this constitution, a collision noise due to collision of the retainer segments is prevented, and the retainer segments are prevented from being stuck due to thermal expansion. In addition, according to the European Patent Publication No. 1408248A2, the retainer segment is formed of polyphenyl sulfide (referred to as “PPS” hereinafter), or polyether ether ketone (referred to as “PEEK” hereinafter).
Here, even when the circumferential range of the clearance is set within the above range, the following problem on which the inventor focused is not solved. FIG. 41 is a schematic sectional view showing a part of the tapered roller bearing 111 when the tapered roller bearing 111 is used as the bearing to support the main shaft of the wind-power generator. In addition, a clearance 115 generated between the retainer segments 101a and 101c is shown with exaggeration in order to be easily understood.
Referring to FIG. 41, a main shaft 110 of the wind-power generator supported by the tapered roller bearing 111 is used as a horizontal shaft. When the tapered roller bearing 111 is used, the retainer segments 101a to 101c revolve in a direction shown by arrows in FIG. 41. The retainer segments 101a to 101c revolve such that the retainer segments 101a to 101c push the adjacent retainer segments 101a to 101c continuously in the direction of the arrows. In this case, the tapered roller and the retainer segment 101a free-fall at a position shown by XXXXI in FIG. 41. In this case, since the retainer segments 101a and 101c collide with each other, the retainer segments 101a and 101c are deformed, and end faces thereof abrade away, and a collision noise is generated, which could considerably lower the function of the tapered roller bearing 111.
When the tapered roller bearing 111 is used as the bearing to support the main shaft 110 of the wind-power generator, since the retainer segments 101a to 101c are large in size, the problem due to the collision at the time of free-falling is serious. Therefore, the above-described range of the clearance is not preferable and the circumferential clearance needs to be smaller. However, there is a limit of reducing the circumferential range of the clearance in the case of the retainer segment formed of the resin due to thermal expansion.